Conventionally, either dye or pigment is used for coloring fibers. In case of coloring with a dye, different dyes (colorants) in structure thereof are used for different kinds of fibers; namely, reactive dyes or direct dyes for cellulose fibers such as cotton and hemp, acid dyes for animal fibers such as wool and silk, acid dyes and disperse dyes for nylon fibers, disperse dyes for polyester fibers, and cationic dyes for acrylic fibers. Depending on the fibers to be colored, these dyes are selected and used for coloring by various dyeing processes.
In addition, when conventional dyes are used for printing a pattern on fibers, a printing paste in which an appropriately selected dye is blended in an aqueous paste is used for printing various designs by a screen stencil. Thereafter, treatments such as drying, steaming, washing with water, soaping, and drying are carried out to obtain colored fibers.
In contrast, when pigments are used for printing a pattern on fibers, a pigment dispersion wherein a water-soluble anionic or nonionic surfactant, a pigment, and a hydrophilic solvent are wet-dispersed by a milling machine that uses glass beads, zirconia beads, titania beads, or stainless balls, is used as the colorant, and this colorant together with a emulsion resin for pigment fixation and a reducer is screen printed, dried, and heat-treated to color the pattern on the fibers.
Therefore, compared to dyes, pigments do not require selection of colorant depending on the kind of fibers, and their processing methods are simple, without requiring steaming process or processes of washing with water and soaping; accordingly, no energy cost is required, and no waste liquid is generated. Thus, this is a safe processing method in terms of environment.
However, pigments have disadvantages in that they require a large amount of emulsion resin for fixing the pigments in order to maintain fastness such as washing fastness. As a result, the texture of the colored fabric tends to harden, and a water-insoluble film is generated due to drying of the fixing agent during processing, leading to a problem of clogging.
Accordingly, coloring with pigments is inferior to coloring with dyes in terms of quality as clothing.
Here, the above-mentioned points relate to methods for coloring fibers using conventional dyes and pigments, in which a screen stencil is required for the formation of design.
In recent years, when coloring fibers, the number of cases of coloring in a small lot and of multiple kinds of products within a short delivery time has increased, resulting in a problem of cost, time, expense and labor of screen stencil making; accordingly, a coloring method by inkjet systems with which printing with no plate-making is possible has been developed, and coloring fibers with dyes has been spreading.
In coloring fibers with dyes using inkjet systems, a dye solution is printed on a fabric that has been pretreated with a cellulose paste, which is then steamed, washed with water and soaped, and dried to give a colored fiber.
In addition, a method wherein a dispersing dye ink is printed on paper by inkjet system then sublimation-transferred on a polyester fiber, has been carried out.
However, since any of these methods use dyes as a colorant, processes of drying, steaming, washing with water, soaping and drying are required after printing. Moreover, only specific fibers can be colored. Therefore, coloring with pigments which enables coloring of any fibers by a simple method has been desired.
Meanwhile, when pigments are used as a colorant in inkjet printing, excellent long-term storage stability of pigments at low viscosity as well as jetting stability such as no clogging of inkjet nozzles are required; in addition to these, upon coloring on fibers, soft texture and good fastness are also required.
As means for solving the above problems in using pigments as a colorant, the following methods (1)-(9) have been proposed.
(1) A method wherein a pigment is fixed to fibers by adding a crosslinking agent to an ink comprising the pigment and a water-soluble polyester or polyamide component as ink components (refer to Patent Literature 1).
(2) An aqueous recording liquid with excellent long-term storage stability, in which its inkjet colorant is prepared as follows: a pigment is dispersed with an organic polymer compound having a neutralized anionic group, then acid deposition is applied by adding an acid, and the pigment surface is coated with the organic polymer compound, then water and a base are added for solubilization to make a micro-encapsulated pigment; which is used as the inkjet colorant (refer to Patent Literature 2).(3) An inkjet printing pigment ink excellent in printing stability, jetting stability, storage stability, and washing fastness, which is prepared as follows: a pigment is dispersed with an organic polymer compound having an anionic group polymerized in an solvent, the solvent is distilled away, then acid deposition is applied by adding an acid, and the pigment surface is coated with the organic polymer compound, then water and a base are added for solubilization to make a micro-encapsulated pigment, to which blocked isocyanate is blended; this ink is used for inkjet printing, then heat treatment is applied to achieve the above excellent properties (refer to Patent Literature 3).(4) An inkjet printing ink comprising a colorant in which a pigment is enclosed by a polymer having a crosslinking structure, a water-soluble organic solvent, and water (refer to Patent Literature 4).(5) An inkjet printing ink, characterized in that at least a pigment, a resin having a carboxylic group, a water-soluble melamine resin, 1,2-alkylene glycol, and water are contained in the ink composition (refer to Patent Literature 5).(6) An inkjet printing ink for fibers, consisting of a pigment, a water-dispersing resin, blocked isocyanate as a crosslinking agent, and water (refer to Patent Literature 6).(7) An inkjet ink, wherein, in the ink comprising an aqueous carrier medium and an insoluble colorant, a core-shell or tetrafluoroethylene emulsion polymer is contained as an additive for improving water resistance (refer to Patent Literature 7).(8) An inkjet ink especially suitable for printing on a fabric, comprising a cross-linked polyurethane dispersion (refer to Patent Literature 8).(9) A material to be recorded by inkjet systems excellent in image clearness, water resistance, light resistance, and color development, wherein, as the ink-receiving layer, a mixture comprising an aqueous emulsion-type acrylic adhesive with a glass transition temperature from −50 to −10° C. and a water-soluble cationic polymer, as its main components, is pre-processed on a polylactic acid fiber (refer to Patent Literature 9).
However, as described hereinafter, the above Patent Literatures 1-9 have the following problems and they are not satisfactory.
In Patent Literature 1, water-soluble polyester resin or polyamide resin is to be used as a pigment dispersant; however, viscosity of the pigment dispersion becomes too high as an ink for inkjet systems, causing a problem of an increase in the viscosity during storage. Accordingly, stable inkjet printing cannot be carried out. In addition, sufficient quality in the fastness and texture as a fiber cannot be provided.
In Patent Literature 2, due to solubilization with a base after acid deposition, large particles are present due to residues of insoluble substances, causing clogging in inkjet system; thus stable and long-term inkjet printing is not possible.
Patent Literature 3 has the following various disadvantages: a) complex processes are required, such as a pigment is once finely dispersed with a solvent, then after acid deposition, an organic polymer compound is fixed on the pigment surface, and a base is blended for solubilization to make a colorant; b) when a blocked isocyanate is blended in this colorant to color fibers and then heat treatment is applied, its fixing strength to the fibers is weak and lack of fastness is expected, and therefore sufficient fastness cannot be obtained; c) after acid deposition of the pigment, in the process of solubilization with a base, aggregation of the pigments may possibly be induced, causing deteriorated stability of the ink during long-term storage, d) the viscosity of the pigment dispersion wherein a pigment is dispersed with these pigment dispersants is high, and when the pigment is dispersed with high concentration, viscosity of the ink increases and an ink with high concentration as a coloring ink for inkjet systems cannot be obtained.
In Patent Literatures 4 and 5, similar to Patent Literatures 2 and 3, a pigment whose surface is coated with a resin by acid deposition or phase inversion is used; therefore, there are the same problems as those in Patent Literature 2 and 3. In addition, since a process of crosslinking the coated pigment by a crosslinking agent is carried out, these inventions are not excellent in terms of clogging, jetting stability and long-term storage stability, similar to Patent Literatures 2 and 3. Moreover, in the invention of Patent Literature 5, a pigment is fixed on a fiber by means of crosslinking the resin having a carboxylic group by a water-soluble melamine resin; and because the water-soluble melamine resin generates harmful formaldehyde, this is not an environmentally good method, and making the ink in one liquid is difficult.
In Patent Literature 6, a water dispersing resin for fixing which also functions as a pigment dispersant is used; however, when a water dispersing resin is used as a pigment dispersant, the dispersion viscosity of the pigment increases, resulting in that the pigment dispersion with low viscosity suitable for inkjet inks cannot be obtained; in addition, since the water dispersing resin forms a water-insoluble film upon drying, time-course stable jetting stability upon inkjet printing cannot be obtained and clogging at nozzle end is predicted; thus, this is not an appropriate ink for inkjet printing.
In Patent Literatures 7 and 8, a core-shell emulsion polymer, a tetrafluoroethylene emulsion polymer or a cross-linked polyurethane dispersion is used. However, these resin emulsions and dispersions form a water-insoluble film upon drying, these are not the inks suitable for inkjet printing, similar to the above Patent Literature 6.
Finally, in Patent Literature 9, a fiber is pretreated with a mixture comprising, as the main components, an aqueous emulsion-type acrylic adhesive and a water-soluble cationic polymer so that the entire surface of the fiber is coated with the resin film; accordingly, it is expected that the fiber has hard texture and its air permeability is inhibited, and clear images cannot be obtained due to repelling of the ink. Thus, the invention cannot provide a satisfactory method as coloring method of fibers.
As described above, in coloring fibers by inkjet systems, coloring with dyes is superior in terms of quality of the colored fabric (texture, fastness), but selection of a dye is necessary depending on the kind of fiber, and there are problems in process efficiency and facility, resource consumption, as well as environmental problems due to generation of waste liquid.
In contrast, coloring with pigments requires a simple process without selection of colorant depending on the kind of fiber, but it has problems such as, many of them are inferior in long-term storage stability, jetting stability, nozzle clogging, and quality of the colored fabric (texture, fastness).
Thus, development of a coloring method of fibers with pigments by inkjet systems, which exhibits no problem in workability, and provides excellent quality of colored fabric (texture, fastness), has been awaited.